The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill acquired	$ 4,895	$ 116
Goodwill	14,479	9,177	$ 9,599	$ 9,089
Aggregate amortization expense	151	$ 88
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill acquired	200
Goodwill	11,600
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	2,900
Jardine Lloyd Thompson Group plc
Segment Reporting Information [Line Items]
Goodwill acquired	4,700
Goodwill	$ 4,695